Molecular diversity of K(V) alpha- and beta-subunit expression in canine gastrointestinal smooth muscles

Voltage-activated K(+) (K(V)) channels play an important role in regulating the membrane potential in excitable cells. In gastrointestinal (GI) smooth muscles, these channels are particularly important in modulating spontaneous electrical activities. The purpose of this study was to identify the molecular components that may be responsible for the K(V) currents found in the canine GI tract. In this report, we have examined the qualitative expression of eighteen different K(V) channel genes in canine GI smooth muscle cells at the transcriptional level using RT-PCR analysis. Our results demonstrate the expression of K(V)1.4, K(V)1.5, K(V)1.6, K(V)2.2, and K(V)4.3 transcripts in all regions of the GI tract examined. Transcripts encoding K(V)1.2, K(V)beta1.1, and K(V)beta1.2 subunits were differentially expressed. K(V)1.1, K(V)1.3, K(V)2.1, K(V)3.1, K(V)3.2, K(V)3.4, K(V)4.1, K(V)4.2, and K(V)beta2.1 transcripts were not detected in any GI smooth muscle cells. We have also determined the protein expression for a subset of these K(V) channel subunits using specific antibodies by immunoblotting and immunohistochemistry. Immunoblotting and immunohistochemistry demonstrated that K(V)1.2, K(V)1.4, K(V)1.5, and K(V)2.2 are expressed at the protein level in GI tissues and smooth muscle cells. K(V)2.1 was not detected in any regions of the GI tract examined. These results suggest that the wide array of electrical activity found in different regions of the canine GI tract may be due in part to the differential expression of K(V) channel subunits.